Effect of 10 years of biofertiliser use on soil quality and rice yield on an Inceptisol in Assam, India

In the present study, field experiments were performed over 10 consecutive years (2006–15) to assess the effects of biofertiliser and enriched biocompost on soil quality, total organic carbon (TOC) and rice yields in an Inceptisol. Experiments were conducted in a randomised block design with four replicates and five treatments: unfertilised control (T1); recommended doses of inorganic fertiliser (T2); biofertiliser with reduced (50%) inorganic N and P fertilisers (T3); reduced (50%) inorganic N and P fertilisers with 1 t ha–1 enriched biocompost (T4); and reduced (75%) inorganic N and P fertilisers with 2 t ha–1 enriched biocompost (T5). T3 improved soil chemical and biological properties with enhanced soil quality index (40%), total P (23%), total K (42%) and fungal (38%) and bacterial (44%) colony counts. T5 significantly improved the carbon pool index (29%) and available nutrients (N, P and K at rates of 37%, 22% and 10% respectively) and increased soil pH (11%), resulting in a higher sustainable yield index (39%) of rice. Fraction 2 (labile carbon) of TOC, total P, available K, microbial biomass carbon and phosphate-solubilising bacteria were key indicators to assess the suitability of these fertilisers in rice cultivation in north-east India.